Res-Parity: Parity Violating Electron Scattering in the Resonance Region Paul E. Reimer y Peter...
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Transcript of Res-Parity: Parity Violating Electron Scattering in the Resonance Region Paul E. Reimer y Peter...
Res-Parity:Parity Violating Electron Scattering in the
Resonance Region
Paul E. Reimery
yWith much help from the talented Res-Parity spokespersons, J.
Arrington, V. Dharmawardane, H. Mkrtchyan, X. Zheng and especially Peter BostedPeter Bosted
Physics: Resonance Structure, Duality, Nuclear Effects in PV scattering
Experiment
Projected Results
Summary:
–“Easy” experiment–Never done before; –Relevant to wider community
2
Parity Violation—A Tool
The cross section can be expressed terms of electromagnetic, weak and interference contribution:
dTotal = d + dweak + dinterference
Asymmetry due to interference between Z0 and
e’
e P
e’
e P
Z0+
Probe using weak interaction instead of EM interaction
EM interaction weights as parton charge squared– Emphasizes up quark
contribution– Weak interaction sensitive to
down and strange quark content
Parity Violation in Resonance Region poorly understood Q2 < 1GeV2 Mproton < W < 2 GeV
3
What is duality and why study it?
In QCD, can be understood from an OPE of moments of structure functions Duality is described in OPE as higher twist (HT) effects being small or cancelling.
c.f. earlier talk by M. Ramsey-Musolf at PAVI06 and
review by Melnitchouk, Ent and Keppel, Phys. Rept. 406 127 (2005), hep-ph/05012017
Gra
ph
ic from
Me
lnitch
ou
k et a
l. P
hys. R
ep
t. 40
6 1
27
(20
05
)
Will higher twist terms cancel similarly with the Z0 probe in parity violation
4
Why Study Duality?
Duality works extremely well for spin-averaged structure function to low values of Q2.
Have a great impact on our ability to access kinematic regions that are difficult to access otherwise
Duality in PV electron scattering will provide new constraints for models trying to understand duality and its QCD origins
Would provide significant limits on the contributions of higher twists to 12 GeV DIS region
Duality also appears to work for spin dependent structure functions
for Q2 > 1 GeV2.
JLab Hall C
data as discussed in
Melnitchouk et al. P
hys. Rept. 406
127 (2005)
5
Resonance Region Asymmetry
For inelastic scattering, ARL can be written in terms of response functions
– A0¼ 6.5 £ 10-4;
– L, T, T0 denote longitudinal, transverse and axial; and
– VL,T,T0 represent lepton kinematic factors.
Sensitive to axial vector transition form factor, GA
N
Details have so far been worked out only for N→∆(1232)– c.f. JLab E04-101 and Jones and Petcov Phys. Lett. 91B 137 (1980)
6
Resonance Region Asymmetry
For inelastic scattering, ARL can be written in terms of response functions
Simple, “toy” model:
depends on sin2W ) Assume sin2W = 0.25 ) VA term disappears
Pure magnetic or electric scattering No strange, charm contributions
ARLRes ¼ -9£ 10-5 Q2 (n/p)
7
Duality for -Z interference?
No reliable model for n/p ratio in res. region: use simple toy model
Will data look anything like this?
Duality good to ~5% in F2, our goal is to measure ALR to ~5% locally and <3% globally
Resonance model
PROTON
DIS model
DATA NEEDED!
8
Resonance Region Asymmetry: (1232)—significant departure from duality
Sato and Lee predict significant departure from Duality for N! ALR = 9£ 10-5Q2(1.075+V+A)
A,V contain axial and vector contributions from neutral current
ALR 2£ larger than duality predictions!
Duality
Sato and LeeE=4 GeV E=6 GeV
9
Physics Goals – Nuclear targets
Parity violating asymmetries over the full resonance region for proton, deuteron, and carbon
Global and local quark-hadron duality in nuclei. – Better precision for global/local duality then proton data
(higher luminosity targets)– W resolution limited by Fermi motion.
First look at EMC effect with Z-boson probe
Important input to other PVES and -scattering measurements on nuclear targets
10
Nuclear dependence (EMC effect)
If photon and Z-exchange terms have – identical dependence on parton distributions and – EMC effect is flavor-independent,
) then we expect NO EMC effect in ARL
If we see nuclear dependence Unexpected (?) physics– Flavor dependence of EMC effect
no sea quark EMC effect seen by Drell-Yan (Fermilab E772)
– Different effect for Z-exchange
If we observe no nuclear dependence important constraint for PVES, -scattering on heavy targets
Res-Parity covers x-region (0.2<x<0.7) where nuclear dependence predicted to be largest in most models
11
Benefits to other experiments
12
Neutrino Oscillation
Resonance region probed by Res-Parity dominates total cross section for 1 < E< 5 GeV, important to MINERA and MINOS
neutrino antineutrino
Major world-wide program to study neutrino mass, mixing Interpretation requires neutrino cross sections in few GeV region on
various nuclei: direct measurements difficult—rely in part on models Res-Parity will constrain these models, especially the isospin
dependence and nuclear dependence
13
Background in Standard Model tests
NuTeV:– Nuclear effects in the weak interaction
(as opposed to EM nuclear effects)– Higher twist effects could explain part of
observed anomaly Møller Scattering:
– SLAC E158 found (22§4)% background correction from low Q2 ep inelastic scattering (mostly resonance region)
– Res-PV will constrain models of the background for future extension aiming at 2% to 3% precision using 11 GeV at JLab (with 1.5 m long target as in E158)
DIS-Parity:– Constraining radiative corrections and Higher Twist effects in current
(E05-007) and future (11 GeV) DIS-PV experiments
14
Experimental setup and expected results
15
Experimental Setup:
Use Hall A HRS spectrometers to simultaneously collect data at two kinematic points
A B C
Graphics courtesy of www.jlab.org
Graphics courtesy of www.jlab.org
Jefferson Laboratory Hall A Plan to maximize overlap in
setup with PV-DIS (E05-007)– Essentially same
experimental setup with different kinematics
16
Experimental Setup
Electrons detected intwo HRS independently
Fast counting DAQ can take 1 MHz rate with 103 pion rejection
C, LD2, LH2 targets(highest cooling power)
4.8 GeV 85% polarized e- beam,80 A, P
b/P
b = 1.2%
Beam intensity asymmetry controlled by parity DAQ
(demonstrated by HAPPEX)
Target density fluctuation, other false asymmetries measuredby the Luminosity Monitor
17
Collaboration
P. E. Bosted (spokesperson), E. Chudakov, V. Dharmawardane (co-spokesperson), A. Duer,
R. Ent, D. Gaskell, J. Gomez, X. Jiang, M. Jones, R. Michaels, B. Reitz, J. Roche,
B. WojtsekhowskiJefferson Lab, Newport News, VA
J. Arrington (co-spokesperson), K. Hafidi, R. Holt, H. Jackson, D. Potterveld, P. E. Reimer,
X. Zheng (co-spokesperson)Argonne National Lab,Argonne, IL
W. Boeglin, P MarkowitzFlorida International University, Miami, FL
C KeppelHampton University, Hampton VA
E. HungerfordUniversity of Houston, Houston, TX
G. Niculescu, I NiculescuJames Madison University, Harrisonburg, VA
T. Forest, N. Simicevic, S. WellsLouisiana Tech University, Ruston, LA
E. J. Beise, F. BenmokhtarUniversity of Maryland, College Park, MD
K. Kumar, K. PaschkeUniversity of Massachusetts, Amherst, MA
F. R. WesselmannNorfolk State University, Norfolk, VA
Y. Liang, A. OpperOhio University, Athens, OH
P. DecowskiSmith College, Northampton, MA
R. Holmes, P. SouderUniversity of Syracuse, Syracuse, NY
S. Connell, M. DaltonUniversity of Witwatersrand, Johannesburg,
South AfricaR. Asaturyan,
H. Mkrtchyan (co-spokesperson), T. Navasardyan, V. Tadevosyan
Yerevan Physics Institute, Yerven, Armenia
Experienced PV collaboration (SLAC E158, HAPPEX, G0)
And the Hall A Collaboration
18
Kinematics and Rates
Rates similar to PV-DIS (E05-007)—see talk by Xiaochao Zheng Pion/electron ratio smaller Low E0 settings in HRS-R, high E0 in HRS-L
Deuterium Kinematics, Rates, etc.
x Y Q2 E0 W e MHz A/A
0.17 0.50 0.6 2.8 2.0 0.6 0.8 4.9%
0.24 0.39 0.7 3.2 1.8 0.2 0.9 4.0%
0.35 0.29 0.8 3.6 1.5 0.1 1.0 3.8%
0.61 0.19 0.9 4.0 1.2 0.0 1.2 3.0%
19
Systematic Uncertainties
Statistical uncertainty--Always statistics limited– 4-6% per W bin– ¼ 2.5% integrated
over full W range
EMC effect: Smaller systematic uncertainties on target ratios (about 1%)
Source A/A
Beam Polarization 0.012
Kinematic Determination of Q2 0.009
Electromagnetic radiative corrections 0.008
Beam asymmetry 0.005
Pion contamination 0.005
DAQ deadtime and pile-up effects 0.003
Pair symmetric background 0.002
Target purity and density Fluctuations
0.002
Pole-tip background 0.001
TotalTotal 0.0180.018
20
Res-Parity Beam time requests
Strong synergy with PV-DIS E05-007 (see talk by Xiaochao Zheng) Non-standard equipment: fast DAQ, upgraded Compton.
Both required for E05-007 (PV-DIS)
E Target PHRS (L,R) time 4.8 GeV LH2 4.0, 3.2 GeV 5 days4.8 GeV LH2 3.6, 2.8 GeV 4 days4.8 GeV LD2 4.0, 3.2 GeV 4 days4.8 GeV LD2 3.6, 2.8 GeV 4 days4.8 GeV C 4.0, 3.2 GeV 6 days4.8 GeV C 3.6, 2.8 GeV 6 days
Pass Change from E05-007 8 hoursPolarization measurements 8 hourse+ asymmetry 8 hours
Total requirement:
30 days of 80 mA, 85% Polarization, parity quality beam
(mostly longitudinal, some transverse to measure 2-photon background)
21
Relative error of 5-7% per bin for 12 W bins shown (8-10% for H)
Local duality (3 resonance regions) tested to <4% (~5% for H) comparable to F2 and g1
Global duality tested to <3%
Ratio of H/D (d/u) and C/D (EMC effect) tested to – 3-4% globally, – ¼5% locally:
Nuclear effects in F2 are >10%
Projected Uncertainties (W Binning)
PROTON
DEUTERON,CARBON
22
Projected Uncertainties ( Binning)
PROTON
DEUTERON,CARBON
Relative error of 5-7% per bin for 12 bins shown (8-10% for H)
Local duality (3 resonance regions) tested to <4% (~5% for H) comparable to F2 and g1
Global duality tested to <3%
Ratio of H/D (d/u) and C/D (EMC effect) tested to – 3-4% globally, – ¼5% locally:
Nuclear effects in F2 are >10%
Sato and Lee1232)
23
Res-Parity: Summary
Easy measurement– Follow lead of PV-DIS@6GeV (E05-
007) New probe of
– Resonance structure– Duality
EMC effect with weak probe– Z0 sensitive to different quark
distribution combination Measure Higher Twist constraints for
PV-DIS Constrain PV background to Møller
Scattering experiments Expt. currently proposed but deferred
24
Easy measurement– Follow lead of PV-DIS@6GeV (E05-
007) New probe of
– Resonance structure– Duality
EMC effect with weak probe– Z0 sensitive to different quark
distribution combination Measure Higher Twist constraints for
PV-DIS Constrain PV background to Møller
Scattering experiments
Res-Parity: Summary
Exploration of Exploration of
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